1.首先备份Ubuntu12.04源列表
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup （备份下当前的源列表）
使用SUDO操作的时候有可能会提示“sudo： 无法解析主机：ebs-40190”，这个时候vim /etc/hosts,新增“127.0.1.1 ebs-40190”就可以了
2.修改更新源
sudo vim /etc/apt/sources.list （打开Ubuntu 12.04源列表文件）
3.把里面的列表替换成下面的列表
deb http://mirrors.sohu.com/ubuntu/ precise main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise main restricted deb http://mirrors.sohu.com/ubuntu/ precise-updates main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise-updates main restricted deb http://mirrors.sohu.com/ubuntu/ precise universe deb-src http://mirrors.sohu.com/ubuntu/ precise universe deb http://mirrors.sohu.com/ubuntu/ precise-updates universe deb-src http://mirrors.sohu.com/ubuntu/ precise-updates universe deb http://mirrors.sohu.com/ubuntu/ precise multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise multiverse deb http://mirrors.sohu.com/ubuntu/ precise-updates multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-updates multiverse deb http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-backports main restricted universe multiverse deb http://mirrors.sohu.com/ubuntu/ precise-security main restricted deb-src http://mirrors.sohu.com/ubuntu/ precise-security main restricted deb http://mirrors.sohu.com/ubuntu/ precise-security universe deb-src http://mirrors.sohu.com/ubuntu/ precise-security universe deb http://mirrors.sohu.com/ubuntu/ precise-security multiverse deb-src http://mirrors.sohu.com/ubuntu/ precise-security multiverse deb http://extras.ubuntu.com/ubuntu precise main deb-src http://extras.ubuntu.com/ubuntu precise main
4.更新源
sudo apt-get update
更新过程中可能会出现“W: GPG 错误：http://extras.ubuntu.com precise Release: 由于没有公钥，无法验证下列签名： NO_PUBKEY 16126D3A3E5C1192”。
这个时候输入“sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 16126D3A3E5C1192”即可解决。